Few thoughts without actuall placing my paws on it. Since you have an inertia switch, I'll assume that the engine is fuel injected. Have you tried pulling some of the plugs as soon as it dies to see if they are actually wet? You could have a bad diaphram in the fuel pressure regulator causing the engine to load up with fuel and die. To check, pull the vaccumm line off of the fuel reulator to see if there is fuel in the line. If so, then the regulator is bad. I would also connect a gauge to the fuel rail's schrader valve to see what the fuel pressure is doing when running good and just as it dies. I would also follow the fuel line from the tank to the fuel rail for any hidden fuel filters. You could also have a bad ingition coil that is breaking down under load.
"Have a good day, and a better one tomorrow"